Electrochromic devices are often used as windows, shades, dividers, mirrors, or electronic displays that change color density or degree of opacity in respect to an applied electric field or current. Such an electrochromic device typically is a multi-layer assembly. Outer layers of the electrochromic device typically are electrodes that are optically clear [i.e. essentially transparent to light in wavelengths of the visual spectrum or at other desired wavelengths]. At least one electrochromic layer is sandwiched between the electrodes. This layer is able to change its degree of color or opacity in response to changes in the applied electric field or current to create visual effects. The electrochromic layer is often an organic polymer film or an inorganic thin film of an electrochromic material. When the voltage is applied across the outer conductors, ions in an electrolyte typically move to the electrochromic layer causing the electrochromic material to change color states. Reversing the voltage moves ions away from the electrochromic layer, restoring the device to its previous state.
An electrolyte is often utilized in an electrochromic device to act as a reservoir for the ions that activate the electrochromic layer and/or provide a medium for transporting ions between a separate ion reservoir material or counter-electrode and the electrochromic layer. A salt such as lithium perchlorate (LiClO4) or trifluorosulfonimide (LiN(CF3SO2)2) may be utilized to provide the ions to activate and deactivate the electrochromic layer. The salt is typically dissociated in a solvent in the electrolyte, freeing the ions for use in activating the electrochromic layer.
Gel electrolytes in electrochromic devices are often preferred because they are less likely to leak than liquids and more stable dimensionally. One gel electrolyte usable in a preferred electrochromic device includes a solid polymer matrix, especially of polymethylmethacrylate (PMMA).
Typically, electrochromic devices exhibit a single color in the visual spectrum when the electrochromic layer is activated, and are otherwise transparent. Such mono-color electrochromic devices are not capable of producing multi-color display logos, architectural patterns, or pictures when the electrochromic layer is activated.